Acetabulum implant

ABSTRACT

The acetabulum is formed of a rigid cup shaped body which has a layer of highly resilient material, such as silicone rubber, secured on the outside. The resilient layer is bonded via a suitable cement to the pelvis and acts to insure against loosening of the rigid body from the pelvis under vibrations while also acting as a cushion.

United States Patent [19] Weber ACETABULUM IMPLANT [75] Inventor:Bernhard Georg Weber, St. Gallen,

Switzerland [73] Assignee: Sulzer Brothers Ltd., Winterthur,

Switzerland [22] Filed: Feb. 1, 1973 211 App]. No.: 328,672

[52] US. Cl. 3/1, 128/92 C [51] Int. Cl. A61f 1/24 [58] Field ofSearch..... 3/1; 128/92 C, 92 CA, 92 R [56] References Cited UNITEDSTATES PATENTS 2,668,531 2/1954 Haboush 128/92 CA 3,064,645 1 1/1962Ficat et a1. 128/92 CA 3,685,058 8/1972 Tronzo 3/1 Apr. 30, 1974 FOREIGNPATENTS OR APPLICATIONS 1,122,634 5/1956 France 128/92 C PrimaryExaminerRichard A. Gaudet Assistant Examiner-Ronald L. Frinks Attorney,Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin 1 1 ABSTRACT Theacetabulum is formed of a rigid cup shaped body which has a layer ofhighly resilient material, such as silicone rubber, secured on theoutside. The resilient layer is bonded via a suitable cement to thepelvis and acts to insure against loosening of the rigid body from thepelvis under vibrations while also acting as a cushion.

7 Claims, 5 Drawing Figures ACETABULUM IMPLANT This invention relates toan acetabulum and more particularly to an implant for placement in thepelvis to function as the normal acetabulum.

I-leretofore, it'has been known to fabricate artificial acetabula orsockets for use as components of a prosthetic hip joint. Generally, theacetebulum which has been used has been secured in a pelvis by means ofa conventional bone cement. However, in the course of time, it has beenfound that the acetabulum has worked loose. It is supposed that the mainreason for this is microvibrations which, when the joint experiencesloading and movement, are transmitted from the acetabulum or socketthrough the bone cement to the bone, probably with the result of localnecroses and/or bone recession.

In order to overcome this problem it has been known to use a shell-likeacetabulum whose edges are secured in the pelvis as disclosed in Frenchpatent specification 1,122,634 and whose shell-like recess, whichreceives either the natural femur head or an artifical metal or plasticsfemur head, is coated with a resilient material to damp impact loadstransmitted via the joint to the bone. However, since the loading on theacetabulum may be as much as 300 kg, this known construction does notlead to a serviceable hip joint. That is, under loads of this nature,the femur head ceases to be able to move at all in a resilient layer orcoating because of excessive friction. The resilient layer musttherefore be given a strong load-resistant contact or sliding surfacewhich, to prevent the resilient material from moving away and beingextruded under load, should bear on the shell-like acetabulum at leastin the fashion of a cover. Unfortunately, this rigid connection of theknown construction leads to impact and vibrations being directlytransmitted from the contact surface to the shell and therefore to thebone. Thus, the resilient layer has been found to have no effect.

Accordingly, it is an object of the invention to obviate loosening of animplanted acetabulum in a hip joint.

It is another object of the invention to avoid microvibrations in theinterface between a pelvic bone and the bone cement used to implant anacetabulum.

Briefly, the invention provides an acetabulum for mounting in a pelviscomprising a rigid body defining an internal recess on one side for afemur head and having an anchorage surface on an opposite side, and alayer of highly resilient material secured to the anchor age surface. Inaddition, the layer of highly resilient material includes a plurality ofexternal grooves and recesses for receiving bone cement when theacetabulum is implanted in a pelvis.

The rigid body can be made of any suitable metal or plastics material.

The term highly resilient material" is to be understood herein asdenoting substances having a final aftercure hardness in Shore A valuesof less than or equal to s 90. As well as being resilient, the materialmust, of course, be compatible with the body and highly resistant to thebody. The material should also have high shear strength and high tensilestrength, more particularly high tear resistance. A silicone rubbercommercially available under the registered trademark Silastic E RTV ofthe Dow Corning International Ltd. company has proved a verysatisfactory substance. Of

course, other substances, such as natural rubber, can be used as thehighly resilient material subject to meeting the conditions set.

The layer of resilient material serves to damp impact as well asvibrations. To this end, the resilient layer must be firmly anchored tothe rigid body which, in turn, must be able to deal with the loads whichoccur which are, as already mentioned, up to 300 kilograms (kg). Inorder to achieve this, the acetabulum is provided with ribs on theanchorage surface, in known manner, as well as anchorage elements whichextend peripherally at a varying spacing from the edge of theacetabulum. These anchorage elements can be, e.g., wire rings brazed tothe ribs.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawingsin which:

FIG. 1 illustrates a side view of a rigid load-bearing acetabulum bodyaccording to the invention;

FIG. 2 illustrates a cross-sectional view of the body of FIG. 1;

FIG. 3 illustrates a side elevational view of a completed acetabulumaccoding to the invention;

FIG. 4 illustrates a plan view of the acetabulum of FIG. 3; and

FIG. 5 illustrates a sectioned view similar to FIG. 2 showing anacetabulum anchored in a pelvis according to the invention.

Referring to FIGS. 1 and 2, the acetabulum body or socket 1 which isrigid and which does not distort permanently when subjected to the loadspreviously referred to, i.e., which is load bearing, is made in knownmanner of a metal alloy compatible with the human organism or of aphysiologically innocuous plastics. The body 1 is formed with apart-spherical internal recess 2 on one side which can be seen in FIG. 2and which is adapted to receive a femur head (not shown). In addition,an outside anchorage surface 3 of the acetabulum body 1 has, in knownmanner, integral ribs 4 disposed in upstanding manner and extending in ameridial direction. Generally, where such a body has been used as theacetabulum per se, often being anchored in the pelvis, the ribs 4 haveserved to prevent relative movements between the socket or acetabulum land the material applied to the socket. Conventionally, such materialhas usually been a bone cement.

Referring to FIGS. 3, 4 and 5, in accordance with the invention, anintermediate layer 5 of highly resilient material is secured to the body1 about the ribs 4. In order to improve the anchorage of theintermediate layer 5 on the surface 3, anchorage elements are providedin the form of wire rings 8'which are secured to the ribs 4, e.g., bybrazing, and which extend peripherally at various distances from theperipheral edge of the acetabulum body 1.

The highly resilient substance for the layer 5 is, for instance, asilicone rubber known under the registered trademark Silastic E RTV ofDow Corning International Ltd. In addition, the outside surface of therubber layer 5 is formed with grooves 6 which extend peripherally andmeridianally as well as with recesses 7.

In order to apply the rubber composition to the anchorage surface 3, thebody 1 is first located at a distance from a mold (not shown) formingthe negative of the outside surface of the layer 5. After intimatemixing with the associated catalyst or cross-linking agent, Dow

Corning RTV catalyst E in the example mentioned, in the specified ratioof, e.g., 1:10, the silicone rubber is introduced into the mold, e.g.,by pouring. Flowability can be increased, if necessary, by means of adiluent.

The silicone rubber specified polymerizes or vulcanizes at roomtemperatures of 25C within 24 hours after the addition of the catalyst,so that a non-shifting anchorage results between the body 1 and thelayer 5. The resilient layer 5 cures much faster at higher temperatures.At room temperatures, the rubber specified reaches its final hardness ofapproximately Shore A 35 to 45 after a few days.

After the material for the layer 5 has reached its final hardness, thecompleted acetabulum 1 can be anchored conventionally in a pelvis (FIG.5) by means ofa known bone cement 12, e.g., methyl methacrylate. Thebone cement 12 which flows into artificial recesses 11 in the pelvis,which recesses 11 extend through the relatively compact bony tissue,forms anchorage pins 13 or projections or the like. The cement 12 alsoenters the grooves 6 and recesses 7, thus giving a non-shiftingconnection between the layer 5 and the bone cement 12. This connectionis very well able to withstand turning and movements along the outsidesurface of the layer 5.

The vibration-damping effect of the intermediate layer 5 very likelydepends upon the very considerable differences between the elasticitymodulii of the body 1, of the components making the anchorage and of thebone. In the example described, these modulii, expressed in kp/mm areabout 20,000 for the metal body, about two or three for the layer 5,about 100 to 200 for the bone cement and about 1000 for the actual bone.There is probably very little transmission of vibratory energy from thevery soft silicone rubber to the less resilient bone cement 12, moreparticularly at the boundary or interface betweenthe layer 5 and thecement 12.

What is claimed is:

1. An acetabulum implant for mounting in a pelvis comprising a rigidbody defining an internal recess on one side for receiving a femur headand having an anchorage surface on an opposite side, and a layer ofhighly resilient material secured to said anchorage surface, said highlyresilient material having a final aftercure hardness in Shore A valuesof less than or equal to 90, the external surface of said layerincluding a plurality of external grooves therein and a plurality ofrecesses therein for receiving a suitable bone cement when implanted ina pelvis.

2. An acetabulum as set forth in claim 1 further comprising a pluralityof integral ribs on said anchorage surface of said body extending intosaid layer and at least one anchorage element extending peripherally ofsaid anchorage surface and said ribs.

3. An acetabulum as set forth in claim 2 comprising a plurality of saidanchorage elements extending at various spacings from the peripheraledge of said body.

4. An acetabulum as set forth in claim 1 wherein said layer is made ofsilicone rubber.

5. An acetabulum as set forth in claim 1 wherein said rigid body is ofcup-shape and said internal recess is part-spherical in shape.

6. An acetabulum as set forth in claim 5 further comprising a pluralityof integral ribs on said anchorage surface extending into said layer.

7. An acetabulum as set forth in claim 6 wherein said layer is made ofsilicone rubber.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3, ,9 DatedApril 30, 197

Patent No.

Bernhard Georg Weber Inventor(s) It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Insert the following on the title page of the patent;

This application is-based on Swiss Patent Application No. 1%7/72 filedFebruary 1, 1972 to which the right of priority is claimed.

Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-5 69 U 5. GOVERNMENT PRINTING OFFICE I969O366-334.

FORM po-loso (10459)

1. An acetabulum implant for mounting in a pelvis comprising a rigidbody defining an internal recess on one side for receiving a femur headand having an anchorage surface on an opposite side, and a layer ofhighly resilient material secured to said anchorage surface, said highlyresilient material having a final aftercure hardness in Shore A valuesof less than or equal to 90, the external surface of said layerincluding a plurality of external grooves therein and a plurality ofrecesses therein for receiving a suitable bone cement when implanted ina pelvis.
 2. An acetabulum as set forth in claim 1 further comprising aplurality of integral ribs on said anchorage surface of said bodyextending into said layer and at least one anchorage element extendingperipherally of said anchorage surface and said ribs.
 3. An acetabulumas set forth in claim 2 comprising a plurality of said anchorageelements extending at various spacings from the peripheral edge of saidbody.
 4. An acetabulum as set forth in claim 1 wherein said layer ismade of silicone rubber.
 5. An acetabulum as set forth in claim 1wherein said rigid body is of cup-shape and said internal recess ispart-spherical in shape.
 6. An acetabulum as set forth in claim 5further comprising a plurality of integral ribs on said anchoragesurface extending into said layer.
 7. An acetabulum as set forth inclaim 6 wherein said layer is made of silicone rubber.